Electromagnetic holding device and demagnetizer



5. KARASICK Aug. 27, 1940.

ELECTROMAGNETIC HOLDING DEVICE AND DEMAGNETIZER Filed Jan. 14, 1937 2 Sheets-Sheet 1 INVENTOR. SAMUEL Kazaa-;cz

ATTORNEY.

S. KARASICK ELECTROMAGNETIC HOLDING DEVICE AND DEMAGNETIZER Filed Jan. 14, 1937 2 Sheets-Sheet 2 IN VENT OR. SAMUEL KARA SICK THERMAYLLY OPERHTE D SW/ TCH ATTORNEY.

Patented Aug. 27, 1940 PATENT OFFICE ELECTROMAGNETIC HOLDING DEVIC'E DEMAGNETIZER Samuel Karasick, Mount Vemon, N. Y.

Application January 14, 1937, Serial No. 120,&06

9 Claims.

This invention relates to combined electromagnetic holding devices, and demagnetizers, as well as to the circuits for Operating the same.

In applicant's copending 'application S. N.

691,()48, now patent No'. 2,138,864, issued December 6, 1938, there is disclosed 'a combined electromagnetic chuck and demagnetizer which is a marked advance in the art altho it has certain limitations. The purpose of the present inveni@ tion is to provide improved and more effective circuits for the operation of such a device, and to overcome the limitations on the circuit design imposed by certain features of the circult described in the said application. As in the case id of the previously disclosed chuck, it is essential that the magnetic circuit be adapted to carry alternating ux, at least in those portions thereof used for demagnetization by' alternating current. It is however, unnecessary in many cases that the entire chuck surface be capable of use as a demagnetizer, since after the interruption of the holding current, it is comparatively easy to slide work, even of hardened steel, along the surface of the chuck to a demagnetizing zone.

The present invention has for a further purpose the provision of a demagnetizing zone at one portion of the work holding surface of a combined chuck and demagnetizer.

In the chuck as described in my previously 3@ mentioned application, it is necessary that each pole be provided with an electrical winding, all

of which are energized for holding on direct current operation, while only half of these poles are energized by alternating current for demagnetization. However, the use of a coil on every pole piece renders it difilcult to provide small poles closely spaced in the work surface whereby numerous small pieces of work, as for example, washers, can be arranged to cover the entire work' surface so that a large number of such pieces can be ground simultaneously. This reduction in pole size, is readily accomplished by the use of energizing coils only on alternate poles of the device, but the application of demagnetizing alternating current is then necessary to' all coils,

as otherwise there would be little or no alternating fiux in alternate poles.

It will be further seen that in a magnetic chuck of the type herein described, the work held is subsequently demagnetized, in the identical conflguration in which it was initially magnetized. That is to say, the geometrical relation of work and poles on the holding part of the cycle of operations is identical with that existing during the demagnetizing portion oi the cycle,`

whereby the elimination of the permanent magnetism impressed on the work while held, is greatly facilitated and the resultant demagnetization is more complete. It will, of course, be understood that the amplitude of the alternati ing flux used for demagnetization must equal or exceed the unidirectional flux utilized for magnetization with the values of uni-directional flux commonly employed in magnetic chucks oi the well known direct current type.

For a clearer understanding of the invention reference is made to the following description and appended claims when taken with the drawings in which Fig. 1 is across section of an electromagnetic chuck suitable for use in the sys- 35 tem of the invention while Fig. 2 is a diagrammatic circuit arrangement suitable for use in the chuck of Fig. 1; Fig. 3 is a cross section of a modified type of chuck suitable for use in a modified type of system of the present invention and 2& Fig. 4 is a diagrammatic showing of a modified circuit arrangement of the invention for use with the chuck of Fig. 3; mg. 5 illustrates a still further modified type of chuck whereas Fig. 6 discloses a diagrammatic circuit arrangement of the invention suitable for use with this last mentioned chuck; Fig. 7 shows a still further modified type of chuck and Flg. 8 is a schematic showing of the' circuit arrangement for energizing the same.

Referring especially to F'ig. 1, the chuck therein disclosed comprises an open top casing having a bottom 5, ends E and side walls (not shown). within the case there is mounted a magnet having a plurality of poles 'I in spaced relaton with the poles extending upward toward the open top of the' case. Alternate poles of the magnet are encircled by energizing coils 8 thereby permitting the magnet poles to be closely spaced so that numerous small pieces of work such as washers can be held on the chuck simultaneously. The 40 top of the case is closed by a work supporting 'plate 9 having a series of pole pieces o mounted therein preferably by being cast in non-magnetic and/or non-conducting material, the spacing of these poles being such that each of them is 45 brought into contact with a pole of a magnet when the work supporting plate is secured on the top of the casing.

The several coils 8 of this chuck are included w in a circuit arrangement disclosed in Fig, 2 which may be selectively operated to energize the several coils 8 by unidirectional current, and subsequently to energize at least a portion of each of the coils by alternating current whereby the work piece supported oh the chuck cau be read- 'o -blades of the switch s are brought into engagevm'ent with the lei'thand contacts the'reot such ily demagnetized. The circuit arrangement includes an alternating current source of a commercial power frequency herein designated AC which is connected under the control of a switch !2 to the primary winding !3 of a transformer T. This transformer in addition to the primary winding !3 has a high voltage secondary winding id and a tertiary low voltage windingit's. The tertiary winding supplies heating current to the cathode I@ of a'rectifler tube i?, over the conductors i& in series. This rectifler tube is of the full wave type having the anodes !3 and enclosed with the cathode !G in a glass envlope containing a gaseous medium so that it is of the gaseous conduction type. The anode i@ of this rectifier is connected over the conductor ?i to the terminal 22 of the secondary winding I of the transformer while the anode 20 is connected over the conductor 23 to a tap se at an intermediate point on the secondary winding. The

energizing coils 8 of the chuck have one oi' their common ende-connected in multiple to the conductor 25 which is connected by the conductor 256 to -tap 2? of the secondary winding i@ at a point thereon midway between the taps22 and 2& thereof; The other common ends of the energizing coils 8 are connected in multiple to a conductor 28 terminating at a contact 23 in the double-pole double-throwswitch s. A tap 30 on each coil 8 is connected 'in multiple to a common conductor 3! which terminates in one blade of the mentioned switch s so that a portion 36 of each of these coils can be energized by alternating current to eil'ect the demagnetization' of the work supported on the'chuckl When it is desired to hold work on the chuck, the blades ofthe double pole switch are brought I into engagement with the right hand contacts such as 29 thereof and the switch -z is also closed to connect'the alternating current sourceto the transformer T, to eflect its energization. The tertiary winding of this transformer supplies heating current to the cathode [0 of the rectifler tube i'|- whfle the portions of the secondary winding between the taps 20 and !T .and 22 and 21 respectively, apply positive voltage alternately to the anodes 20 and I! so that tube I 'I functions as a tull wave rectifler. The out-. put of the rectifler Supplies direct current over the 'conductors 25 and 25 through the entire length of the coils 0,' conductor 20, switch contact 29, lower blade of switch &conductor 32 to the cathode circuit. I! and s are closed in' the position last'men'- tioned, direct current is supplied to thecoils 0 to energize them thereby retaining the work pieces against the pole pieces ll in the work; support 9. I

When it is deslred merely 'to releasejwo-k pieces which do not become permanently magnetized by being supported on the chuck, the' i switch !2 can be opened or else 'switch S can be moved to an intermediate position so that 'direct current is no longer supplied to the coils of the chuck. However, if the work material such as hardenedsteel has been held on the chuck it is necessary to demagnetize it. before it can be removed from the chuck. In order to eifect de'magnetization of such material the movable as 33. With the switch in this position and is supplied to the lower portion 38 only oi each As long-as the switches series.

amator.

of the coils. This alternating current is applied in a circuit' traceable from the upper terminal 35 of the secondary winding i i of the transformer, rheostat R, contact 33 of the switch S, upper blade thereof, conductor 3i, branch conductors 36, lower portion 36 of coils 8 in multiple,

work piece, it is preferably moved transversely' of the pole pieces !0, in effect applying a decrementally reversing fiux to the work piece. The portions 36 of the coils 8 as well as the difierence in potential across the terminals 2? and 35 of the secondary winding of the 'transformer' are so proportioned that an aiternating magnetomotive force is applied to the poles of the magnet and to the pole pieces it, equal or greater *than the direct'magnetomotive force applied thereto. It has been found that for any single coil such as 8, an alternating voltege at least twenty times the directvoltage is required to produce a suitable amplitude of alternatng flux because of the inductive reactance of the coils 8. It would of course, be possible to utilize the entire winding of the coils B when energized by either direct or alternating cmrr ent. However, if the entire length of the coils 'were used, that is, if the taps 30 thereon were omitted and conductor 3i were connected to the upper terminals of the coils 8 while the lower terminals'remaln connected to the conductor 25. the difierenoe in potential across the conductor Et and the contact 33 would need to be about twenty times 4 the direct curre'nt output of the rectifler, for

example, if a direct voltage of flty volts were used, then the required alternating voltage would be approximately one' thousand volts. such a voltage however, is so high as to be dangerous and would require careful and costly insulation of the windings of the coil 8. If taps 30 are positioned at approximately the midpoints of the In the present arrangement the altemating current-in the lower portions o! the coils will be about twice the direct 'current in the entire winding of these coils. This tactor must be taken into consideration in designing the coil. Obviously the taps 30 may be located at various positions along the windings of the coils: and

the voltage applied thereto adjusted accordingly. The chuck illustrated in Fig. 3 is subst'antially identical with the chuck disclosed in mg. 1 except that the coils 40 and 'M thereot have no intermediate tap suchas the tap 30 on the coils 8. The 'remaining parts of the chuck are designated by the same reference characters asapplied to the foregoing chuck.

In the circuit arrangement shown in Fix. 4 the coils 40, ll of the chuck are all connected in This arrangement producw a more emcient rectifler circuit, since it increases the direct voltage applied to the magnets. However, one of these coils, such as ll canbe energizedwith an a ernating voltage induced across the' entire length of the secondary winding of the transi'ormer. When the four pole double throw switch S! is closed 'to its lefthand position the coil 4| is energized by the entire secondary voltage induced in' the secondary winding of the transformer, while all of the coils are energized in series by direct current when this switch is closed to its righthand position. The rectifier utilized in this arrangement is also of the full wave gaseous conduction type and the circuits of the power device in which it is included, are similar to those disclosed in Fig. 2 and need not be turther described.

In the operation of this circuit arrangement, when it is desired to retain the work on the work surface of 'the chuck, the four-pole, double-throw switch is moved to close its righthand contacts so that the output of the rectifler is applied through the upper-most pair of blades of the switch and conductors 45 and 48 to all the coils 40 and 4i in series. However, when it is desired `-to demagnetize the work piece on the chuck, the .switch is moved to close its lefthand contacts whereby the entire voltage developed in the se'condary winding of the transformer is applied over the conductors 44 and 45, the two lowerrnost blades of the switch and thence through conductors 45 and 41 to the terminals of the coil ti. At the same time the work-piece is moved along the surface of the chuck across the portion thereof energized by the coil 4i which is now carrying alternating current so that the workpiece is demagnetized. In the arrangement illustrated eight coil windings are provided and the entire secondary voltage oi the transformer is applied to the coil 4! so that the ratio of the alternating voltage to direct voltage appliedto this coil is about twenty to one and hence adequate alternating flux will be developed in its related pole piece.

The modified form of the chuck illustrated in Fig. 5 also includes a casing having a bottom 5 and end walls the casing beingvopen at its top. The magnets i which in this instance comprise a plurality of pole extensions are also mounted within the casing with the poles oi' the magnets extending upward. Each leg oi the magnet is encircled by a coil comprising two independent sections &9 and 50. The work supporting top plate closes the top oi 'the casing and has' the pole pieces i@ mounted in spaced reiation thei-ein in non-magnetic and/or nonconducting material. a pole extension of the magnet i'n this chuck, and the entire 'surface oi the top plate thereof is used tor holding the work and ior demagnetizng the same.

The circuit arrangement for energizing the coils 49 and 59 in the chuck is illustrated in Fig. 6 and comprises a source of alternating current and a source of rectiiied or direct current developed by the power device disclosed within the broken lines. The several parts of this power 'device are identical with those already described and the various parts thereof are designated by the same reference characters as applied to the' corresponding power devices already described. This power device is connected to the coils of the chuck by a double-pole double throw switch S3 so that alternating or direct current can be selectively applied to the chuck. When the blades of this switch are moved into engagement with the righthand contacts thereof, rectified current is supplied over the-conductor 3| through the windings 50 and 49 in series, conductor 51,

Each pole piece engageslower blade of the switch, conductor 32 to the 21 for application to the coils 50, is higher than the voltage of the rectified current.

It will be apparent from the ioregoing description that`the winding of the coils 49 and 5@ and the difference in potential between the tap 21 and the terminal 35 of the secondary winding of the transformer can be so chosen in relation to the direct voltage applied as to produce an alternating fiux adequate to demagnetize the work piece supported on the chuck.

The modified type of chuck shown in Fig. 7 is similar to that already disclosed in Fig. 1 and the corresponding parts thereof are designated by the same reference characters, In this chuck each alternate extension only of the magnet is encircled by an energizing coil such as or 55.

A circuit arrangement which is suitable for use with this chuck, is disclosed in Fig. 8 and includes a power device for supplying rectied current to the several coils of the chuck and for applying alternating current to these coils to eiiect demagnetization of the work supported on the chuck. 'This power device is identical with the power devices already described. A threepole double-throw switch SC is provided to con- ,nect'either the re'ctified output of the power de- Vice to the coils of the chuck or to connect the alternating'output of this device to these coils. With the switch moved to its righthand position to engage its several Contacts, rectied current is supplied over the conductor 5? from the rectifier, contact 53 of the switch, blade 59 thereof, conductor tii, coils 55, conductor ti, blade 62 of the switch, contact 63 thereof, conductor G i, contact 85 of the switch, switch blade 56 thereof, conductor ti, coils 56, conductors 69 and i@ to connect the two groups of coils in series across the output oi the rectier. When the switch s is closed to the left, the direct current circuit last-described is-broken and alternating current ows irom the terminal 35 of the secondary winding *of the transformer through rheostat R to the contact '32 of the switch thence through blade 59 thereof to conductor 6@ and contact 73 of the switch. The current divides, one half thereof owing over conductor %El to the coils '55 and the other half of the current fiowing through the middle blade &E of switch to conductor E? and thence through the coils 56. The current passing through coils 'returns over conductor si while that passing through coils 56 returns over conductor'le. i conductor ti is connected to the top blade 62 of switch SG and cur-` rent therefrom fiows to conductor iii through blade 62 when the switch is in its lefthand position. Thiis it will be seen that on alternating current all coils 55 and 56 are connected in parallel. Since there are two poles per coil, and since the two groups of coils 55 and 56 must be equal in number, it follows that in a chuck of this type, the total number of poles must be an integral multiple of four.

Cold cathode gas filled discharge devices 14 v aaaoor and 15 are respectively connected between the conductors to which the common ends of the coils 55 and 56 are connected. The switch jaws 63 and 65 are longer than the others on the righthand side of the switch S& so that when this switch is opened from its righthand Contacts, the direct current circuit' is broken first at the switch contact 58. Thus the resulting surge voltage induced in the coils 55 and 56 which remain 10 momentarily connected in series through switch r contacts se and 55, breaks down the discharge devices and the energy stored in the magnetic fields of the coils is dissipated in a momentary discharge through said tubes'thereby greatly re 15 ducing the surge voltage strains otherwise ap- 20 alternating current circuit when the interior of the chuck rises to an objectionably high temperature which might occur if the 'switch S remained closed in its lefthand position inadvertently for a very long period. It will be appreciated that this possibility of overheating may arise from the eddy current losses in the magsuch netic circuit generally termed iron losses. a thermostatic switch is applicable to the alternating circuits of the arrangements of Figs. 2, 4 and 6.

While the group of coils 55, has been shown connected in multiple in Fig. 8 and the group of coils 56 has similarly been connected in multiple,`

magnetizing said work.

'It should be mentioned that the pole pieces ID are preerably made of laminated pieces of material having high permeability. The magnets 'i are also preferably made of laminated ferrous material.

It will be noted `that a rheostat R is included in one of the leads oi the alternating circuit of each chuckand when it is desired to demagnetize the work material, the alternating current g@ applied to the alternating current coils., of the several. chucks may be 'gradually decreased by means of this rheostat thereby applying a decrenentaily reversing flux to the pole pieces of .the severd chucks.

gg What I claim is:

1-. Ina holding device for pieces of magnetizable material on which work is to be done, a work support, a plurality of pole pieces of magnetiza ble material terminatin'g'in a surface of said sup- 50 port in a given pattern, means unidirectionally.

to magnetize said pole pieces to grip a piece of material against said surface, and means including a source of altemating' current 'for reversing repeatedly at a commercial power frequency 55 the magnetization of said same pole pieces for demagnetizing said piece ofmaterial in the same flux pattern that magnetized it, said unidirectional magnetizing `means comprising a coil placed upon each'alternate pole piece, and said w means for reversingly magnetizing said pole pieces comprising all of the coils aforesaid, said coils being further connected in two groups, the alternate coils being connected together in-one `coil group and the other coilsin a second coil en group and means for connecting said groups in series for unidirectional -magnetization and means for connecting said groups in multiple with said alternating current source for demagnetization.

'2. In a work holding device, spaced magnetizable pole pieces arranged in a given pattern, a work support having a surface in which said pole pieces terminate, magnets having poles, each pole engaging a pole piece, a pair of coils about each of certain of 'said poles, means including a source' of unidirectional current to energize said coils for magnetizing said magnets and pole pieces to retain a work piece of magnetic material on said surface, a source of alternating current and means including said alternating current source and a single coil of each pair energized therefrom for reversingly magnetizing said pole pieces whereby said work piece is demagnetized.

3. In a work holding device, spaced magnetizable pole pieces arranged in a given pattern, a

work support having a surface in which said pole pieces terminate, magnets having poles, each pole engaging a pole piece, a pair of coils about each of certain'of said poles, means including a source of unidirectional current to energize said coils in series for magnetizing said magnets and pole pieces to retain a work piece of magnetic material on said surface, a source of alternating current and means including said alternating current source and a single coil of each pair energized in series for reversingly magnetizing said pole pieces whereby said work piece is demagnetized.

4. In awork holding device and demagnetizer, spaced magnetizable pole pieces, a work support having a surface in which said pole pieces terminate, magnets having poles, each pole engag'- ing a pole piece, a coil about each of certain of said poles, each alternate coil being connected together in one coil group and each of the other alternate coils being connected together in a second coil group, means including a source oi' unidirectional current supplied to said groups of coils in series for magnetizing said magnets and pole pieces to retain a work piece' on said device, a source of alternating current, and means including said alternating current source applied to said groups of coils connected in multiple for reversingly magnetizing said magnets and said pole pieces whereby said work piece is dema.,- netized. i

5. In a work holding device and demagnetizer, spaced magnetizable pole pieces, a work support 'having a surface in which said pole pieces terminate, magnets having poles, each pole engaging a pole piece, a coil about each of certain of' said poles, each alternate coil being connected into one of two groups of coils, means including a source of unidirectional current supplied to said groups of coils in series for magnetizing said magnets and pole pieces to retain a work piece on said device, a source of alternating current, means including said alternating current source applied to said groups of coils connected in multiple for reversingly magnetizing said magnets and said pole pieces whereby"? said work piece is demagnetzed( and surge voltage discharge means connected across the terminals of said coils.

6. In an arrangement of the' class described, a combined magnetic holding and demagnetizing device, acommercial alternating current source for Operating said device, said device' comprising a core having core elements, atleast a portion of said elements being each provided with an energizing coil, the impedance of each coil at the requency of said source being several times as great as the direct current resistance thereof, said coils being arranged into a plurality of coil groups, means for rectifying said alternating current, means for connecting said coil groups in series to said rectifying means, a transformer connectible to said alternating current source, means for ccnnecting said coil groups in parallel to said transformer, said transformer having such a transformation ratio that the total electromotive force per coil group is materially greater than when said coil groups are connected to said rectiying means, and means eective at Will r'or connecting said coil groups either to said rectiiying means or to said transformer.

7. In an arrangement of the class described, a combined magnetic holding and demagnetizing device, a commercial alternating current source for Operating said device, said device comprising a core having core elements, each alternate element only of at least a portion of said elements being provided with aii energizing coil, the impedance of each coil at the frequency of said source being several times as great as the direct current resistance thereof, said coils being arranged into a plurality of coil groups, means :for rectiiying said alternating current, means for connecting said coil groups in series to said rectifying means, a transformer connectible to said alternating current source, means for connecting said coil groups in parallel to said transormer, said transformer having such a transformation ratlo that the total electromotive force per coil group is materially greater than when said coil groups are connected to said rectifying means, and means effective at will for connecting said coil groups either to said rectifying means or to said transformer.

8. In an arrangement of the class described, a combined magnetic holding and demagnetizing device, a commercial alternating current source for Operating said device, said device comprislng a core having core elements, each alternate element only of at least a portion of said elements being provided with an energizing coil, the impedance of each coil at the requency of said source being several times as great as the direct current resistance -thereof, said coils being arranged into a plurality of coil groups, means for rectifying said alternating current, means for connecting said coil groups in series to said rectifying means, a transformer connectible to said alternating current source, means for connecting said coil groups in parallel to said transormer, the inductance of the coil groups connected in series being materially greater than the nductance of the coil groups connected in parallel, said transformer having such a transormation ratio that the total electromotive force per coil group is materially greater than when said coil groups are connected to said rectifying means, and means effective at will for connecting said coil groups either to 'said rectifying means or to said transformer.

9. In a work holding device and demagnetizer, spaced magnetizable pole pieces, a work support having a surface in which said pole pieces terminate, magnets having poles, each pole engaging a pole piece, a coil about each of certain of said poles, the alternate coils beingconnected in multiple into two groups of coils, means including a source of unidirectional current for supplying direct current to said groups of coils in series for magnetizing said magnets and pole pieces to retain a work piece on said device, a source of alternating current, and means including said alternating current source for supplying alternating current to all of the coils of said groups connected in multiple with each other as a second group for reversingly magnetizing said magnets and said pole pieces whereby said work piece is demagnetized.

SAMUEL KARASICK. 

